Fig. 1. Tk-RadA encodes an intein with an active HEN domain.

(A) Schematic representations of precursor RadA (pRadA; top) splicing to form both intein and mRadA. The precursor RadA is composed of N-extein, intein, and C-extein denoted in blue, red/orange, and blue, respectively. The region of the intein containing the HEN domain is shown in orange. aa, amino acids. (B) In vitro RadA-mediated DNA cleavage demonstrates that HEN activity targets inteinless alleles of TK1899. Tk-RadA^WT does not cut its own sequence (TK1899^WT) (left) but can cut inteinless allele of RadA from T. kodakarensis (TK1899^{ΔIntein-encoding sequences}) (middle). HEN activities are compromised in the Tk-RadA^(373–381)A variant wherein HEN active site residues are altered to alanines (right). The intact DNA target and resultant cleavage product(s) are represented by a star and a triangle, respectively.